I am offering this advice because I have been burned by Verizon and their competitors over that last 20 years. Give yourself the time and power to fight back!
#1 Rule: Don't just threaten to cancel - be prepared to cancel.
Sometimes it's just better to switch companies. When I agree to a one or two year contract, I schedule a reminder on my calendar to check what the competitor is offering new customers two weeks before the contract ends. Then I call and say I want to cancel my service. They will not let you go that easily! They will make you an offer to stay... If they give me a similar price, I stay. (I have to really be prepared to switch, because sometimes they just won't give me as good a deal.) Sometimes, I have to make the switch...
#2 Rule: When you change providers, overlap them.
Have both installed and running for about two weeks, so you can cancel your new service when they break their promises and try to rip you off. Then pay attention and fight immediately. The last two times I switched internet providers, I had them install the new service in only part of my house while the old one was still running in another part of my house. Even though I had to pay for two extra weeks of the old service, it saved me money!
For example, I just did this again two weeks ago. Comcast couldn't match what FiOS was offering for internet, so I ordered FIOS online to get the best deal and cancelled Comcast internet effective 3 weeks later (which was already paid for in my previous bill - I cancelled autopay.)
Houses that never had FIOS get the ONT equipment installed for free, but my house used to have FIOS, so their system automatically removed a technician visit when I entered my address. I immediately called and explained that my ONT was no longer operational, so somebody would have to come out AT NO CHARGE OR I WOULD CANCEL THE ORDER. The customer service rep set up a tech install and told me they would waive the fee.
The tech came, and I said not to do anything for which I would be charged. He agreed and repaired my ONT and I now had working internet through a FIOS gateway in one room. Two hours later I was emailed a bill with a $100 charge for the technician visit. I called immediately and said to cancel everything if I was going to be charged, because that was not what I had been promised. (I still had Comcast internet up and running, and I told them that.) The customer service rep explained that they could not waive that fee until my bill was "officially" in their system. He told me to give them one week for processing. I said "Right now I have in writing that I will be charged and only your word that I will not be charged. I am giving Verizon one week to fix this or I cancel." and I set my calendar. Today, was one week later. I checked my account and there was an "official" bill - and it had the $100 charged on it. So I called and reviewed everything that had happened and explained one last time that I would cancel immediately unless the was fixed. She found NO NOTES in my account that I had ever been promised anything. I told her the days and times of my previous calls. She checked with her supervisor and told me so sorry, tough crap, they were going to charge me the extra $100 - nothing I could do about it. So I said to cancel my service, and she said "Okay." I asked where to return my FIOS router and while she was looking up the address for the nearest location, guess what... Her supervisor had "heard our conversation" and decided to remove the charge. And they did it in my account immediately.
I only got that charge removed because I was REALLY cancelling their service. I was able to REALLY cancel because I STILL had internet from their competitor. (In fact, I am using Comcast internet to type this post.)
I had to go through similar fights when I switched from FIOS to Comcast five years ago. (I had to threaten to not keep the new Comcast then, because of extra charges.) It was GREAT to not be held hostage.
Fighting with these folks sucks. But I spent two weeks fighting in 2014 and then it was all over - I got two years of exactly what had been promised - great service at a great price. (And it was easier to get good deals every year after that.)
Now I have NEW internet that works well (I have tested it to be sure) a price guarantee that is good (my bill is exactly what it was supposed be) and no extra charges.
I am HAPPY and THE FIGHT IS OVER for at least a year.
(By the way, I rent a router/gateway for only the first month and then buy one after I am sure I am keeping the service.)